1. Field of the Invention
The present process is directed to an improvement in the preparation of zero-valent nickel complexes which typically are used as catalyst for the production of dinitriles. More particularly, the present process is directed to the recovery of a zero-valent nickel catalyst promoted by an organoborane after the catalyst and promoter have been used in the production of adiponitrile by the hydrocyanation of 3- and/or 4-pentenenitriles.
2. Description of the Prior Art
U.S. Pat. No. 3,496,218 issued on Feb. 17, 1970 describes in general terms a process for the preparation of dinitriles especially adiponitrile by the hydrocyanation of non-conjugated, ethylenically unsaturated organic compounds, e.g., 3- and/or 4-penteneitriles using certain nickel complexes as catalysts. The catalysts are promoted by organoborane compounds such as triphenylborane. A wide range of process conditions and relative amounts and types of reactants are disclosed.
A particularly useful form of zero-valent nickel catalyst is described in U.S. Pat. No. 3,766,237 issued on Oct. 16, 1973. The patentees disclose the use of an excess of the triarylphosphite ligand in the hydrocyanation along with the addition of certain ethers to improve the yield and increase the pounds of product which can be made per pound of catalyst consumed.
U.S. Pat. No. 3,903,120 issued on Sept. 2, 1975 discloses an improved process for the preparation of zero-valent nickel complexes with aromatic phosphorus compounds using a phosphorus halide as a catalyst to increase the reaction rate of elemental nickel. It is also disclosed that organic mononitriles and/or dinitriles increase the reaction rate when used as a solvent.
U.S. Pat. No. 3,773,809 issued on Nov. 20, 1973 discloses a process for separating organic phosphorus compounds and their metal complexes, e.g., the above-described catalysts, from organic nitriles by extracting the product fluid with a paraffin or cycloparaffin hydrocarbon solvent at 0.degree.-100.degree. C. The organic phosphorus compounds and their metal complexes are contained predominantly in the hydrocarbon phase and the organic mononitriles and dinitriles are predominantly contained in a separate phase.